One of known processes for producing an unsaturated dicarboxylic acid imide compound which is used in, for example, the preparation of an addition type imide resin comprises cyclizing an unsaturated amide acid compound. The cyclization may be conducted by, for example, a heat cyclization process described in JP-A-57-159764 (the term "JP-A" as used herein means a "published unexamined patent application") or a chemical cyclization process described in JP-A-53-23396.
The heat cyclization process literally comprises undergoing cyclization by heating to give approximately 93% by weight of a highly pure unsaturated dicarboxylic acid imide compound. However, this process requires a very long reaction period of time such as about 72 hours at the longest. Further, the cyclization is conducted through dehydration in a high energy state, which sometimes results in self-polymerization of part of the formed unsaturated dicarboxylic acid imide compound to thereby give a polymer. Consequently, the addition type imide resin prepared from this unsaturated dicarboxylic acid imide compound is somewhat disadvantageous in, for example, moldability.
The chemical cyclization process comprises undergoing cyclization by using a dehydrating agent such as acetic anhydride. Since this process can be completed at a low temperature within a short period of time, the obtained unsaturated dicarboxylic acid imide compound contains a small amount of polymer components. However, this process has some disadvantages such that the purity of the obtained unsaturated dicarboxylic acid imide compound is limited to approximately 90% at the highest.